ERBB2 and breast cancer: Likewise, an increase in histone acetylation has been observed at lysine residues, such as H3K9ac (associated with HER2-enriched tumors, poor prognosis, and reduced OV), H3K18ac (associated with hormone receptor-positive malignant breast tumors), and H4K12ac (found in adjacent normal breast tissues to luminal and triple-negative malignant breast tumors) [196,197,198].